Catalytic cracking operations are commercially employed in the petroleum refining industry to produce useful products, such as high quality gasoline and fuel oils from hydrocarbon-containing feeds. The endothermic catalytic cracking of hydrocarbons is most typically practiced in accordance with two known catalytic cracking operations, namely, fluid catalytic cracking (FCC) and moving bed catalytic cracking.
Generally, both fluid catalytic cracking and moving bed operations are commercially practiced in a cycling mode. During these operations the hydrocarbon feedstock is contacted with hot, active, solid particulate catalyst without added hydrogen at rather low pressures of up to about 50 psig and temperatures sufficient to support the desired cracking. As the hydrocarbon feed is cracked in the presence of cracking catalyst, to form more valuable and desirable products, undesirable carbonaceous residue known as "coke" is deposited on the catalyst. The coke contains carbon as well as metals that are present in the feedstock.
In FCC operations, the catalyst is a fine powder of about 20-200 microns in diameter. The fine powder is propelled upwardly through a riser reaction zone, fluidized and thoroughly mixed in the hydrocarbon feed. The hydrocarbon feed is cracked at high temperatures by the catalyst and separated into various hydrocarbon products. The coked catalyst particles are separated from the cracked hydrocarbon products, and after purging, are transferred into a regenerator where the coke is burnt off to regenerate the catalyst. The regenerated catalyst then flows downwards from the regenerator to the base of the riser.
The cycles of cracking and regeneration at high flow rates and temperatures have a tendency to physically break down the catalyst into smaller particles, called "fines" which have a diameter of up to 20 microns as compared to the average diameter of the catalyst particle of about 60 to about 90 microns. Excessive generation of catalyst fines increases the cost of catalyst to the refiner.
Commercial catalytic cracking units include cyclones and electrostatic precipitators to prevent fines from becoming airborne. Additionally, the catalyst particles cannot be too large in diameter, or the particles may not be sufficiently fluidized. Therefore, the catalysts are maintained under 120 to 150 microns in diameter.
In determining the unit retention of catalysts, and accordingly their cost efficiency, attrition is a key parameter. While the size of the particles can be controlled relatively easily by the initial spray drying of the catalyst, if the attrition index is high, then the average particle size may quickly diminish. In such situations, the catalytic cracking unit may, therefore, produce a large amount of the 0-20 micron fines which should not be released into the atmosphere.
Additionally, deposition of coke on the catalyst particles is generally considered undesirable for two reasons: First, it inevitably results in decline in catalytic activity to a point where the catalyst is considered to have become "spent"; and second, coke generally forms on the catalyst at the expense of the more desired liquid products. To regenerate the catalytic activity, the hydrocarbon residues of the coke must be burnt off of the "spent" catalyst at elevated temperatures in a regenerator.
Current worldwide refinery trends indicate a continuing need to process heavier feed stock. As a result, many refineries will be processing feedstock containing resids or deeper cut gas oils which have high metals contents. The enhancement of octane produced in catalytic cracking operations is an important goal in the preparation of zeolite containing catalysts. The environmental regulations in the United States and abroad, and the phaseout of lead additives for gasolines in both the U.S. and abroad, requires refineries to use catalysts which produce increased octane gasolines from heavier metals contaminated feedstock.
Accordingly, one object of the present invention is to provide a zeolite containing catalyst preparation which has improved attrition resistance.
Another object of the present invention is to provide attrition resistant catalysts which also provide the benefit of increased octane performance.
A further object of the present invention is to provide attrition resistant and octane enhancing catalysts containing REY type zeolites.
A still further object of the present invention is to provide attrition resistant and octane enhancing catalysts without further increasing coke or dry gas make.